Theoretical Study On The Quantum Anti-Zeno Effect In Nuclear ? Decay

Frequent measurements may inhibit the evolution of an unstable quantum system,this is called quantum Zeno effect(QZE).This peculiar quantum phenomenon has attracted widespread interest,and the QZE has played an important role in the fields of condensed matter and quantum information up to now.For example,it can be used to suppress intramolecular forces,to protect quantum information,and to realize direct counterfactual communication.In contrast,the frequent measurements may also accelerate the evolution of an unstable quantum system,this is called quantum anti-Zeno effect(AZE).In recent years,both the QZE and AZE have been experimentally proved in trapped ion systems,cold atom systems,and nanomechanical oscillator systems.It is a very meaningful question in nuclear physics whether frequent measurements could change the decay rate of an unstable nuclear system,namely,whether the QZE or AZE could be observed in nuclear decay.The AZE in nuclear ? decay has been predicted by Kofman and Kurizki in[Nature(London)405,546(2000)].In this thesis,we take a detailed study of the AZE in different types of nuclear ? decay by using the time-dependent perturbation theory and combining with the related theories of AZE based on the prediction.It is found that the AZE indeed dominates the nuclear ? decay,namely the ? decay rate of an unstable nucleus,which is under frequent measurements,is obviously faster than the exponential decay rate,which is under no measurement.Moreover,the AZE in the case of ?+/?-decay is more significant than the case of orbital electron capture(EC),and it is also found that nucleus with a small? decay energy(such as 3H)is more favorable to observe AZE in experiments.In chapter one,at first,we introduce the theoretical and experimental works of the QZE and AZE.Then the energy spectrum,the type of decay,and the decay energy of ?decay are introduced in detail.Finally,the exponential decay law of an unstable system is introduced,and it is also introduced in detail for the related work on the deviation behavior of the early decay of an unstable system from the exponential decay behavior,especially the deviation behavior of the early ? decay.In chapter two,we first introduce the Fermi theory of the ? decay.Then the integral expression of the effective decay rate is derived in detail by using the timedependent perturbation theory and combining with the related theories of AZE.Finally,the integral expression is changed into a general expression of the effective decay rate,which is dependent on the spectral density function,by mathematical derivation.In chapter three,we first discuss and give the specific form of the spectral density function in ? decay.Then the expressions of effective decay rates,which are dependent on the measurement interval,of ?+/?-and the EC decay types are obtained by a detailed derivation.Finally,a detailed calculation of the ratio between the effective decay rate and the natural one is presented for the nuclei,which are from different decay types,namely,3H,60Co(?-type),22Na,106Ag(?+type)and 18F,57Co and 111Sn(EC type).Furthermore,it is suggested that 3H may be a possible suitable experimental candidate to observe AZE in experiments.In chapter four,we give a systematic summary about this master thesis.Finally,we present a outlook for future studies.